Chevy Tahoe Problems - HELP! - PeachParts Mercedes-Benz Forum

gmercoleza · #1 08-18-2006, 09:33 AM

My buddy has a 4WD Tahoe, I'm not sure what year but it's most likely a 1998 to 2003. Has about 90K on the clock. It is exhibiting a few of issues:

Check Engine Light About a month back he had codes read at AutoZone which indicated TPS and one other part which I don't remember, probably MAF. He replaced both, but the TPS light has come back twice. I warned him that generic codes are not necessarily remedied by plug-and-play parts replacement. What are the common failure points?

Dieseling Holy cow, this thing diesels like crazy! Happens when applying heavy throttle while moving. Sounds like an SDL for about a second, then levels out. He runs 87 in it, I believe the manual specifies it. I told him to put 93 in it for a couple of tanks to see if it levels out. It has been 105 here after all. However, shouldn't everything automatically detune if preignition is detected? Maybe his piezoelectric (knock) sensor is blown? But wouldn't that throw a code or invoke limp?

Engine knock When the dieseling levels off, a faint knock can briefly be heard while still under load. Valve train has been ruled out as the noise is not present when revving unsprung and is most apparent under moderate to heavy load. I'm thinking mains or rods? How can that be, when it only has 90K? Is that a known issue on these engines?

As a side point, he is running 5W30 in this vehicle - yikes! This is a severe duty vehicle, often being idled for extended periods in the heat with the A/C on. I don't know what his manual says, but I'm almost certain that 5W30 in an engine with 90K on the clock running in 105* heat is not ideal. I told him to run 15W40 DELO or 20W50 in it. I am not attempting to start another oil thread here (flame suit on), but I do think 5W30 is a little light. Any thoughts?

Mechanically speaking, these Tahoes are supposedly fairly reliable. While Consumer Reports gives thumbs down to the 4WD, it is only due to consistent rollovers in avoidance maneuver testing; the 2WD is actually a "Recommended" vehicle as it exhibits average reliability.

I am aware of the famous piston slap issues plaguing 98 and up GM engines and wonder if some of the engine noise is related. I don't see direct reference to the Tahoe at http://www.pistonslap.com, but I don't exactly know which engine is under his hood either. Is this similar to the BMW alusil issues? Will this engine be seizing shortly?

TIA to all the experts...

gmercoleza · #2 08-18-2006, 10:45 AM

I considered the EGR, but I'm pretty certain EGR will throw a code. Besides, in my experience EGR related issues tend to manifest themselves as pinging under light throttle, low RPM while cruising on the highway.

But you might be on to something. Testing with a MityVac is probably in order. It might be beneficial for him to try cleaning the EGR out. Also maybe running some water or top end cleaner into the engine several times and letting it sit overnight each time. I successfully cured pinging in my Dad's Volvo a few weeks back using this method. After reviewing some more info on the GM piston slap issue, there could be top-end buildup that is causing the preignition. Who knows - this could also be throwing the CEL?

rwthomas1 · #3 08-18-2006, 12:08 PM

In Texas heat I would say a 10W-40 or 15W-40 far more appropriate for a GM V8 with 90K on it. When was the last time the spark plugs were changed and are they the correct plug? Incorrect plugs can cause all sorts of strange knocking/pinging if they are to hot in the heat range. I would be tempted to change the oil and the plugs and then tow at least 5,000lbs around for at least 100miles. The hot/hard pulling usually blows out carbon, etc. that accumulates from light use. RT

gmercoleza · #4 08-18-2006, 12:19 PM

Not sure about the plugs. I'm guessing with 90K maybe it's never been tuned up yet. You are right though - I am reminded of an old Dodge Van with the bulletproof slant-6 I used to have that would detonate and sometimes continued running even after you shut it off. Pulled the plugs and they were the wrong heat range. Were probably glowing red hot and preigniting the A/F mixture.

I emailed this thread to the owner, so he is monitoring it.

I told him to try cleaning the top end, test the O2 duty cycle, run Techron or Chevron 93 through the gas tank, even check compression and EGR since these are all cheap or free.

Thanks for the suggestions, please keep 'em coming!

gmercoleza · #5 08-20-2006, 08:56 AM

Bump - Ttt

TheDon · #6 08-20-2006, 09:47 AM

bring it in and tell gm.. its slapping and make them dissasemble the engine and inspect it . on their bill

Gil · #7 08-20-2006, 10:27 AM

Not that this helps your buddy much, but do yourself a favor and take Consumer Reports with a BIG grain of salt. After the way they targeted Suzuki a few years back I wouldn't always trust their conclusions.

Why? They deliberately rolled a Samurai during very unrealistic testing while ignoring easier rollovers from other vehicles like the Ford Bronco II. Consumer Reports (Consumer's Union) had just spent millions on their new corporate headquarters and was looking for a soul to steal to help pay for it. Suzuki had cash, but not so much cash and political influence as to be better protected from stupid lawsuits. Consumer's Union stood to gain a piece of the profits from any suits against Suzuki (under a certain legal doctrine I won't bore you with). So, they publish a scare tactic safety report, get people who think they're affected to sue Suzuki, collect their share of the profits and look like heroes in the process. The American way. But I digress...

Maybe what they said about the 4wd Tahoe was true, but after the Samurai debacle I have to wonder under what circumstances they got it to roll.

gmercoleza · #8 08-20-2006, 12:27 PM

I definitely take CR with a grain of salt and not as gospel. I use them only as a guide along with other sources like Edmunds, J.D. Power, Consumer guide, etc. With that said, I also do not take anecdotal evidence as gospel and realize that often hundreds or even thousands of subjects need to be tested before an evaluation can be formulated. In this regards, I believe CR's actuarial-based analyses are pretty much right on the money. I am familiar with the situation surrounding the Samurai, the tests of which was a big deal when I was a teenager. I have seen the videos and in my opinion they were performed fairly. True, there were other vehicles that were in fact more prone to tipping than the Samurai (Ford Bronco II is a good example). And it might rightly be said that the Samurai was just a patsy due to Suzuki's relatively recent foray into automotive manufacturing. But that didn't change the fact that the Samurai was itself prone to rollovers. I know there are plenty of members here that love the Sammy and otherwise find them mechanically simple and easy to work on.

CR has toned down their implications of "sure death with purchase" in recent years. Their tests of the Mazda Tribute / Ford Escape SUV conducted within the last year are a notable example of CR lauding a vehicle's positive attributes, including reliability, while simply not recommending it due to rollover test results.

Validity of CR test results has been debated here ad nauseum. My point in bringing this up in the first place was that the Tahoe, rollover test results aside, is in fact considered to have average mechanical reliability. So it was surprising to me that, at 90K, it would exhibit issues usually reserved for "high mileage" vehicles.

Gil · #9 08-20-2006, 12:32 PM

CR recently (two years ago) published an anniversary edition special where they highlighted the Suzuki case and the tests, which were not found to be so kosher. Suzuki said enough is enough and sued them to stop highlighting the biased tests. As far as I know, they won. Score one for the good guys.

P.S.: I can understand Edmunds, thats good info, but J.D. Power? You're not referring to the "initial quality" surveys, I hope? All that says is that within the first three months, new car buyers still like their cars - how helpful is that?

gmercoleza · #10 08-20-2006, 12:34 PM

Can we brush this attempted thread hijack aside and get back to the matter at hand - any other ideas on this Tahoe? Anyone? Bueller?

DR.DIESEL · #11 08-20-2006, 05:29 PM

Sounds like carbon build up to me from cheap gas and extened idling.
I had a similar issue with my 99 Gm truck.
GM makes a dealer product called "Top End Cleaner".
This stuff is like Liquid Plumber for carbon. We use a ton of it here at the
MB dealership.
I would.
1. Use GM top end cleaner
2. Add pure Techron additive to fuel
3. Change plugs
4. Cap, rotor, and wires (if equipped based on year of truck)
5. Drive and recheck. Knock sensor may be weak or failed.
6.GM recommends 5-30 for fuel economy, I would avoid 20-50 however.

Good luck,
DR.D

gmercoleza · #12 08-20-2006, 06:55 PM

Quote:

Originally Posted by Gil

P.S.: I can understand Edmunds, thats good info, but J.D. Power? You're not referring to the "initial quality" surveys, I hope? All that says is that within the first three months, new car buyers still like their cars - how helpful is that?

The point I am making is that, in an attempt to avoid adopting narrow, myopic viewpoints, I try to be objective and consider ALL opinions and sources of information. That includes friends, coworkers, the dealer service department, TV shows, and yes even J.D. Power. I think the fact that I am asking for Chevy advice on a Mercedes forum speaks volumes.

Are we done here?

TheDon · #13 08-20-2006, 07:01 PM

Quote:

Originally Posted by gmercoleza

I think the fact that I am asking for Chevy advice on a Mercedes forum speaks volumes.

^_^ theirs the problem.. chevy
did you try a chevy tahoe forum?they should know alot , kinda like the members of mercedes based forums ya know

gmercoleza · #14 08-20-2006, 07:10 PM

Quote:

Originally Posted by DR.DIESEL

Sounds like carbon build up to me from cheap gas and extened idling.
I had a similar issue with my 99 Gm truck.
GM makes a dealer product called "Top End Cleaner".
This stuff is like Liquid Plumber for carbon. We use a ton of it here at the
MB dealership.
I would.
1. Use GM top end cleaner
2. Add pure Techron additive to fuel
3. Change plugs
4. Cap, rotor, and wires (if equipped based on year of truck)
5. Drive and recheck. Knock sensor may be weak or failed.
6.GM recommends 5-30 for fuel economy, I would avoid 20-50 however.

Good luck,
DR.D

Thanks for the info. I already had him pick up a couple cans of GM top end cleaner from the Chevy dealer. I have had good success with that product. I think he might be using it over the next couple days and will be checking with him. I also recommended Techron to him, and I believe he picked up some new plugs. Looks like we're on the same page.

As for the oil, GM and other manufacturers began recommending lower weight oil in order to report a small percentage increase in government fuel economy testing with little care for the long-term effects. With the increasing popularity of leasing and trading in vehicles every 3 or 4 years, this is understandable and even makes some sense. The owner plans on keeping the vehicle as far as I know, so running a low weight oil in this hot climate just isn't prudent.

gmercoleza · #15 08-22-2006, 12:10 AM

OK, we have some major problems here. He cleaned with 2 cans top end cleaner, everything went great. He described the process he used and it appears he did it properly. He also changed the oil afterward for fear of dilution, used DELO 15W40. Here's where it gets tricky.

Today after work I helped him run a compression test. Results were about 145 to 150 or so across cylinders 1 through 7. On cylinder 8, we got 138 which seemed kind of low. We put about 1 or 2 teaspoons of oil in the cylinder via a tube, and after about a minute took another compression reading. This time it came back at 152.

<>

Since the plugs were out, we replaced with brand new OE plugs from the dealer, properly gapped at .040. Started it up, and everything appears great! No pinging, very smooth idle, smooth powerful acceleration. It wasn't like this the other night when we test drove it. It's like a new truck. There is an ever so slight knock sound still present; I think it may be more noticeable now that the dieseling sound is gone. <>

Here's the kicker - it is leaving a thick cloud of burning oil smoke behind it! The smell is suffocating and the smoke is really thick. It is definitely blue and smells of burning oil. We drove the car in a mix of local streets and highway for about 20 to 30 minutes and the smoke did not go away. This is definitely not remnants of the top end cleaner because he lives about 20 minutes for me, plenty of time to blow out the top end cleaner.

Any ideas?

Here's my/our theory: Cleaning carbon revealed flaws in cylinder #8 which is now drawing up oil due to worn rings which no longer seal.

By the way, no more check engine light, at least in the 20 to 30 minutes we drove it.

Any ideas?